What version of Automation Studio do you have? The easiest way to do this with a non-Windows HMI is to setup the OPC server and tags on the B&R side and then it's just a regular OPC connection on whatever HMI you use.
If you make a Windows based HMI, B&R has a free .Net API that you can use which is super easy and a training manual that explains it all (TM712, google it and you'll find it). For a long time, you didn't even need to change the B&R project to be able to read and write to process variables with the API, might still be true.